Lung Mechanics and Ventilation

Question 1

What is the difference between ventilation and respiration?

Answer 1

Ventilation is the process of inspiration and expiration i.e the mechanical movement of the chest

Respitation is the chemical process of gaseous movement

Question 2

What is tidal volume?

Answer 2

The volume of air being moved in and out during quiet inspiration and expiration

Question 3

How does our body control breathing?

Answer 3

Neurones in the respiratory centre of the brain generate automatic rhythmic impulse

(can be overridden)

Question 4

What is the relationship between pressure and volume?

Answer 4

Inverse relationship

increase in volume ⇔ decreases pressure

Question 5

Which muscles are invovled in quiet inspiration and how?

Answer 5

Diaphragm (70%) contracts and flattens

External intercostal muscles (30%) contract pulling chest wall laterally and superiorally

Collectively incresing volume of throacic cavity and decreasing pressure

Question 6

How is air expelled from the lungs in quiet expiration?

Answer 6

passive process of relaxing the muscles used in inspiration

Volume of lungs decreases due to elastic recoil

Question 7

How are lungs kept against the chest wall despite their tendancy for elastic recoil?

Answer 7

Pleural fluid between visceral and parietal pleural froms a seal between the lung and throacic wall

Question 8

What is the resting expiratory level?

Answer 8

The point at the end of expiration, before the next inhalation where the lung is subject to equal and opposite forces

Question 9

During the repiratory expiratory level, descibe the forces acting on the thoracic wall

Answer 9

inward: lungs pull up and in due to elastic recoil

outward: chest wall favours outward movement at rest

diaphragm: pull down due to passive stretch

Question 10

What is the interpleural space?

Answer 10

The space between the pleura of the lungs

Question 11

What is significant about the pressure within the intrapleural space and why?

Answer 11

The pressure is always negative relative to atmospheric pressure

Due to elastic recoil of lungs pulling visceral pleura inwards and the chest wall pulling parietal pleura outward

Question 12

What happens if the pleural seal is broken?

Answer 12

Pleural Effusion

Negative pressure in intrapleural space will draw air from atmosphere into the space causing the lung to collapse

Question 13

What is the inspiratory reserve volume?

Answer 13

The extra volume of air that can be inhaled into the lung during forced inspiration

Question 14

What is the expiratory reserve volume?

Answer 14

The extra volume of air that can be forced out of the lungs during forced expiration

Question 15

What is the residual volume?

Answer 15

The volume of air left in the lungs, even after forced expiration

Question 16

Which accessory muscles can be used in inspiration?

Answer 16

• Sternocleidomastoid
• Scalene muscles
• Serratus Anterior
• Pectoralis Major

Question 17

Which accessory muscles can be used in expiration if it requires more effort?

Answer 17

• Internal intercostals
• Abdominal wall muscles

Question 18

When might accessory muscles be used for respiration?

Answer 18

Either during exercise or if a disease affects the lungs

Question 19

What is compliance?

Answer 19

The abiltiy of the lungs to stretch

High compliance = very stretchy

(or volume change p/unit pressure)

Question 20

In order for the lungs to stretch what 2 properties of the lung must be overcome?

Answer 20

• Elastic tissue in the lungs
• Surface tension of fluid lining alveoli

Question 21

What is the effect of fluid lining alveoli?

Answer 21

Fluid creates surface tension that limits their expansion

Question 22

How does the lung overcome the surface tension of the alveoli?

Answer 22

The lung secretes surfactant which has detergent properties that disrupts the fluid surface tension

Question 23

Which cells secrete surfactant?

Answer 23

Type 2 pneumocytes

Question 24

What size of alveoli does surfactant have the biggest effect at disrupting surface tension?

Answer 24

smaller alveoli

Surfactant molecules are closer together so more effective at disrupting surface tension

Question 25

What is the effect of reducing surface tension on small alveoli?

Answer 25

Reducing surface tension prevents pressure rising within the alveoli as a result of smaller volume…

… Preventing small alveoli collapsing into large alveoli

Question 26

Without surfactant, what would be the effect of having different sized alveoli?

Answer 26

Question 27

Why do premature babies often go into respiratory distress?

Answer 27

Surfactant isn’t produced until fetus >25 weeks

without surfactant surface tension of alveoli remains high and small alveoli collapse into large making it hard for the infant to breath

Question 28

In isolation, which airways have the highest reistance to flow?

Answer 28

The smallest diameter airways

Question 29

Why is the combined resistance of small airways low?

Answer 29

As the small airways are arranged in parallel

compensates for high individual resistance

Question 30

Where is resitance highest and lowest in a normal pair of lungs?

Answer 30

Highest: The upper respiratory tree (trachea & large bronchi)

Lowest: smaller airways